William B. Euler

Suppression of toxic compounds produced in the decomposition of lithium-ion battery electrolytes

Liquid electrolytes typically used in commercial lithium-ion batteries are comprised of lithium hexafluorophosphate in carbonate solvents. This electrolyte undergoes thermal decomposition at moderately elevated temperatures (80-100°C), encountered in the normal operation of these rechargeable power sources, to quantitatively generate highly toxic alkylfluorophosphates. The decomposition occurs via an autocatalytic mechanism initiated by trace impurities of water or alcohol. The thermal decomposition is inhibited in the presence of lithium metal oxides frequently used as the cathode of lithium-ion batteries or Lewis basic additives.

Hybrid solar cells based on single-walled carbon nanotubes/Si heterojunctions

Photovoltaic devices based on single-walled carbon nanotubes (SWNTs) and n-silicon heterojunctions have been fabricated by a spray deposition process. We provide direct evidence that nanotubes serve as an active photosensing material involved directly in the photon absorption process as well as contributing to charge separation, transport and collection. The characteristic band of the SWNT band in the photoconductivity spectrum matches the S(11) absorption band of semiconducting SWNTs of 7,6 chirality. Centrifugation of the SWNTs provides two fractions. The sediment fraction exhibits a conversion efficiency ( approximately 1.7%) higher by a factor of eight compared to the supernatant fraction. SEM images and conductivity measurements show that the SWNT network morphology of the sediment fraction has longer and thicker nanotube bundles forming highly porous films, accounting for the enhanced conductivity and higher transparency.

Fluorescent polymer-porous silicon microcavity devices for explosive detection

Conjugated polymers entrapped in porous silicon microcavity have been studied as optical sensors for low volatility explosives such as trinitrotoluene. The fluorescence spectra of entrapped polymers were modulated by the microcavity via a spectral “hole” that matches the resonance peak of the microcavity reflectance. Exposure of the porous silicon microcavity containing entrapped polymer to explosives vapor results in a red shift of the resonance peak and the spectral hole, accompanied by the quenching of the fluorescence. This multiplexed response provides multiple monitoring parameters, enabling the development of an optical sensor array for the detection of target explosive vapor.

Hybrid solar cells based on porous Si and copper phthalocyanine derivatives

We demonstrate a solar cell based on n-type nanoporous Si (PSi) filled with copper phthalocyanine (CuPC) and its derivatives (including a discotic liquid crystal form). The CuPC device shows conversion efficiency up to 2% under white light illumination (20–30mW∕cm2), distinct from cells filled with CuPC derivatives with alkyl chains attached to the core. It is concluded that a critical issue for efficient photocarrier generation is the distance between the CuPC core and the PSi surface. Both organic and inorganic components contribute to photoinduced charge transfer and transport processes. The influence of the PSi structure and pore filling on the solar cell performance is discussed.

Extended Huckel calculations on the Pi system of polyaniline

Abstract The pi molecular orbitals of aniline are used in a tight-binding calculation, within the extended Huckel methodology, to find the energy band structure of head-to-tall polyaniline. The highest occupied band, the 3b 1 , is also the widest band with width=1.7eV. This band can be depopulated either by oxidation or protonation to give a metal-like conductive state. Alternately, oxidation can lead to quinoid-like defect sites along the polymer chain that give midgap states that could be responsible for conductivity. The lowest unoccupied state is the localized 2a 2 orbital positioned 3.0eV above the top of the 3b 1 band. Because of the localized nature of this state, reductive doping should not be an effective method for improving the conductivity of polyaniline.

Synthesis and characterization of oligonaphthylamines

Abstract Colored oligonaphthylamine films were electrochemically synthesized in an aqueous acidic medium containing KI. Five colored films were obtained: clear, green, blue, purple and pink. CV and IR data suggest that the oligonaphthylamine products are 1,4-coupled via amine/imine linkages. The observed acid-base behavior, electrochemistry and UV-Vis spectroscopy of the oligonaphthylamine films are similar to those of poly/oligoanilines and known naphthylamine derivatives. The clear oligonaphthylamine film is the most reduced oligonaphthylamine species, containing all 1,4-amine linkages. The pink deprotonated oligonaphthylamine film is the most oxidized species containing the most imine linkages. The blue and purple protonated oligonaphthylamine films correspond to intermediate oxidation states. However, Raman spectroscopy of the green oligonaphthylamine film reveals it to be an oligonaphthylamine-I − 3 complex.

Electromechanical actuation of composite material from carbon nanotubes and ionomeric polymer

An actuating system composed of nafion ionomeric polymer coated with single-walled carbon nanotubes electrodes was studied as an electromechanical actuator. The actuator gives a sizable mechanical response to low voltages (turn-on voltage of approximately 2.5 V) under open-air conditions, i.e., in the absence of a surrounding supporting electrolyte. The actuator is active under both dc and ac bias and has a strong resonance at low frequencies which is dependent upon the size of the actuator. The actuator was studied using Fourier transform infrared and vis-NIR spectroscopies, cyclic voltammetry, and by the current-time response under an applied step voltage. An analytical model is proposed to understand the electrical behavior, which is consistent with the spectroscopic results.

Carbon nanotube-Si diode as a detector of mid-infrared illumination

We report a room temperature mid-infrared photodetector based on a carbon nanotube-silicon heterojunction nanostructure. The observed mid-infrared band (8–12 μm) in the photocurrent spectrum is consistent with the estimated band gap energy of semiconducting multiwall nanotubes (15 to 30 nm diameter). The fast response time (16 ms) and small temperature change (∼10−8 K) upon infrared light suggest that the photocurrent response is not due to bolometric effect. We determined that the primary mechanism of the photocurrent in this spectral range is associated with photon absorption of semiconducting multiwalled carbon nanotubes followed by charge separation at the interface, their transport, and collection at the external electrodes.

SYNTHESIS AND CHARACTERIZATION OF PYRIDINE END-CAPPED OLIGOAZINES

Abstract A new group of controlled chain length oligoazine analogues with pyridine end groups are synthesized and characterized.

Photophysics of Carbon Nanotubes Interfaced with Organic and Inorganic Materials

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